The present invention relates to a roller bit including a number of legs, preferably three, that has a pin rotatably journalling a cutting cone, that bearing races for the cutting cone are arranged on the pin, and that a sealing site for a sealing element, preferably an O-ring, is arranged at the inner end of the pin and means for locking the cutting cone relative to the pin in its axial direction. The invention also relates to a leg and a cutting cone separately.
According to prior art the sealing site of the pin for an O-ring is usually integral with the leg. However, it is also known to design the sealing site for the O-ring as a separate element, see e.g. U.S. Pat. No. 4,452,539. The aim of this structural design is to avoid corrosion of the sealing surfaces for the O-ring, i.e. sealing surfaces that according to prior art are designed integral with the leg. To solve this problem the arrangement of separate sealing surfaces for the O-ring is indicated. What is characterizing for these separate sealing surfaces is that they consist of an anti-corrosive material that is higher in the electromotive series than the surfaces of the pin that the separate elements are attached to.
The separate sealing surfaces can either be provided through plating with an anti-corrosive material or through a separate element being welded thereto, e.g. by gas-plasma welding.
The aim of the present invention is not primarily to avoid corrosion of the sealing site for the sealing element but the primary aim of the present invention is to design the sealing site as a separate sealing insert, that in a simple way can be attached to the pin.
An essentially great advantage of the present invention, including a separate sealing insert, is the freedom of material, i.e. one can choose a material selection having the wanted characteristics.
A further advantage of a separate sealing insert is that the abrasion particles can not propagate to the sealing site as easily as if it is integral with the leg.
A further advantage of a separate sealing insert is that a more even compression of the sealing element can be achieved.
A further advantage of a separate sealing insert is that it can be subjected to a number of different treatments, e.g. surface treatment, deep rolling, hardening, without one having to consider the leg. This in its turn means that the manufacturing of the leg can be carried out without considering the specified claims of the sealing insert.